Alumoxanes are the products of partial hydrolysis of hydrocarbylaluminum compounds and have been found useful in a variety of chemical reactions, including catalyst components for polymerization catalysts and especially as a component for catalysts in the preparation of high-activity, homogeneous Ziegler catalysts, as is described, for example, in U.S. patent application 501,740, filed June 6, 1983.
Various processes are known for the preparation of alumoxanes, the simplest being to add water in predetermined amounts and under controlled conditions to a hydrocarbylaluminum compound as described in U.S. Pat. No. 3,242,099. Alumoxanes can also be obtained, for example, by the action of water vapor on a benzene solution of a trialkylaluminum (J. Am. Chem. Soc. 90, 3173 [1968]) by using lithium dialkylaluminates as the organoaluminum starting compound (J. Am. Chem. Soc., 89, 173 [1967]). Other known methods for preparing alumoxanes include oxidizing aluminum-hydrocarbon compounds with lead dioxide (J. Organomet. Chem., 43, 81 [1972]), treating an alkylaluminum with alkyldistannoxanes [(R.sub.3 Sn).sub.2 0 ]in place of water (Racanelli, P. and Porri, L., Europ. Polym. J., 6, 751 [1970]) and hydrolyzing alkylaluminums with copper sulfate containing water of crystallization as suggested in European patent application No. 0035242.
In Australian Patent No. 20861/83, Kaminsky, et al. discloses a method of preparing alumoxanes by contacting aluminum salts containing water of crystallization with a trialkylaluminum. It is taught that the alumoxanes are obtained in higher yields and greater purity.
In many of these processes, because of the highly exothermic nature of the reaction between the water and the hydrocarbylaluminum, the reaction can easily get out of control or even become explosive. While the use of CuSO.sub.4.5H.sub.2 O as a source of water provides for the slow addition of water, thus reducing the risk of local excesses of water and thereby reducing the probability of a runaway or explosive reaction, the method suffers from some drawbacks. For example, the Cu(II) may be reduced to Cu(I) or even to metallic copper during the reaction with an alkylaluminum, such as trimethylaluminum. This can lead to the introduction of sulfate groups and other undesirable types of functionalities, as well as copper, into the alumoxane preparation. The alumoxane product, therefore, prior to use as a component of a catalyst system in a polymerization process, must be filtered, purified and recrystallized, since otherwise adverse conditions will exist during the polymerization, and the quality and quantity of the polymer will be adversely affected. Another disadvantage associated with CuSO.sub.4.5H.sub.2 O in preparation of alumoxane is the low yield which is on the order of about 30% relative to the aluminum trialkyl employed.
Some of these problems can be essentially eliminated, if one employs hydrated salts as the source of water in the preparation of alumoxanes, such as methyl alumoxane wherein the metal component is not reduced during the alumoxane preparation. Such a solution is disclosed in U.S. Pat. No. 4,665,208, issued to Welborn on May 12, 1987.
The disadvantage associated with using hydrated salts is that the heterogeneous solution of trialkylaluminum, hydrated sale and hydrocarbon still have the potential for a violent reaction during the formation of the alkylalumoxane even though the danger is greatly reduced. Consequently, there is still a need for a process which can safely and efficiently produce hydrocarbylalumoxanes.
Attempts to react boron oxide with trialkylaluminum without the intermediate step of producing trihydrocarbylboroxine have been unsuccessful. However, the reaction of boron oxide with trialkylboron to yield trialkylboroxine is disclosed in "The Reaction of Triorganoboranes with Boric Acid" by G. F. Hennion, et al., Journal of American Chemical Society, vol. 79, p. 5194 (1957). This reaction proceeds according to the following stoichiometry: EQU B.sub.2 O.sub.3 +R.sub.3 B.fwdarw.(RBO).sub.3
It has also been disclosed in "New Synthesis of Trialkylboranes," by G. C. Ashby, Journal of American Chemical Society, vol. 81, p. 4791 (1959), that trialkylboroxine produced in the above reaction can be reacted with trialkylaluminum to yield alumina and trialkylborane according to the following stoichiometry: EQU (RBO).sub.3 +2R.sub.3 Al.fwdarw.3R.sub.3 B+A l.sub.2 O.sub.3
In a similar reaction scheme published by J. G. Ruff entitled "A New Preparation of Some Dimethylalumino Derivations of Boron," Journal of Organic Chemistry, vol. 27, p. 1020 (1962), alkylboroxine was reacted with trisdimethylaluminoalane to yield a byproduct generally identified as [(CH.sub.3).sub.2 NAlO.sup.- ].sub.x. The stoichiometry of this reaction was described as follows: EQU 2(RBO).sub.3 +3Al[N(CH.sub.3).sub.2 ].sub.3 .fwdarw.(RB[N(CH.sub.3).sub.2 ].sub.3 +3/X[CH.sub.3) .sub.2 NAlO.sup.- ].sub.x
Similarly, Koster U.S. Pat. No. 3,049,407 teaches a process for synthesizing boron alkyls and highly active aluminum oxide. The synthesis consists of reacting an aluminum trialkyl and boroxol system first at a temperature below 100.degree. C. and then at a temperature of between 150.degree. C. and 220.degree. C. The first stage reaction proceeds as EQU 2(RBO).sub.3 +6AlR.sub.3 =6BR.sub.3 +2(RAlO).sub.3
This is followed directly and without disturbing system concentrations by the second stage which can be described as EQU 2(RAlO).sub.3 +(RBO).sub.3 =3BR.sub.3 +3Al.sub.2 O.sub.3
The overall process yielding the boron alkyl and aluminum oxide is the combination of the two reaction steps or EQU (RBO).sub.3 +2AlR.sub.3 =3BR.sub.3 +3Al.sub.2 O.sub.3
However, none of these references mentions that a mixture of linear and/or cyclic alkylalumoxanes can be safely and efficiently produced from trihydrocarbylboroxine and trialkylaluminum.